There are numerous applications where it is necessary to measure an amount of fuel in a container.
U.S. patent application Ser. No. 10/955,485, “Method and system for encoding fluid level” filed by Holcomb et al. on Sep. 30, 2004 and issued as U.S. Pat. No. 6,992,757, describe a float riding on the surface of a fluid. The float is mechanically coupled to a rotating encoder disk which is segmented with optically transparent and opaque regions. A set of light emitting diodes (LEDs) are aligned with photo sensors on the other side of the disk So that the fluid level can be encoded as the disk rotates as the float moves up and down.
U.S. patent application Ser. No. 10/800,484, “Optical fluid level monitor” filed by David Corven et al. on Mar. 15, 2004, describes an optical sensor that includes a display, a light pipe optically connected to the display and extending to a level of interest in the reservoir, where the light pipe is formed from a material having a refractive index higher than air's refractive index and less than or equal to the liquid's refractive index; and a light optically connected to the light pipe. The light pipe can be a glass or plastic rod, or a bundle of optical fibers.
U.S. patent application Ser. No. 10/267,965, “Fluid container with level indicator, and fluid level indicator assembly for a fluid container,” filed by Lee et al. on Oct. 9, 2002, describes fluid level sensor that includes a visual display of a fluid level in a container using multiple capillary tubes terminating at different vertical levels from one another in the container.
U.S. patent application Ser. No. 10/265,954, “LCC-based fluid-level detection sensor” filed by Shi et al. on Oct. 7, 2002 and issued as U.S. Pat. No. 6,949,758, describes a fluid level sensor based on light communication channel (LCC) technology. One end of the LCC is connected to a signal source while another end is connected to a sensor. The LCC is dipped in a fluid container and a signal propagates and undergoes internal reflection through the LCC towards one of its ends which is connected to the sensor. The fluid level is detected by measuring an intensity of the signal reflected with the LCC that reaches a sensor.
U.S. Pat. No. 5,852,946, “Method and apparatus for detecting fluid level” issued Cowger on Dec. 29, 1998, describes a fluid level detector for providing a signal indicative of fluid level in a fluid container. The fluid level detector includes a first light conduit portion for providing light to fluid within the fluid container. A second light conduit portion is provided for receiving light provided by the first light conduit portion. Also included is a light path extending from the first light conduit portion to the second conduit portion. The light path has a light path length, which varies with an amount of fluid within the fluid container. The light path length variation produces light intensity variation at the second conduit portion which is indicative of fluid level in the fluid container.
U.S. Pat. No. 5,747,824, “Apparatus and method for sensing fluid level” issued to Jung et al. on May 5, 1998, describes an array of infrared LEDs and an array of photo sensors are positioned vertically in a cassette. A vertical line on which the LEDs are arranged is substantially parallel to a direction in which the fluid level is within the cassette. The LEDs are aimed upwardly at an angle of approximately 20 degrees from horizontal so the a beam of light does not penetrate the fluid/air interface.
The Jung system can be distinguished according to a number of characteristics. First, for each level to be measured that system requires a light source and sensor pair for each fluid level to be detected. Second, the system cannot detect how far below or above the fluid level is for a single source/sensor pair. Third, for accurate readings of multiple levels a baffle is required to block energy at various angles. For fluids that can scatter light, adjacent sensors need to be properly oriented.